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Helcionelloida
page 1
Helcionelloida
thumb|Yochelcionella cyrano thumb|Pelagiella atlantoides Helcionelloida is an extinct group of ancient molluscs (phylum Mollusca). These are the oldest known conchiferan molluscs, that is, they had a mineralised shell. Some members of this class were mistaken for Monoplacophorans. The class was erected by Peel in 1991.